Aviation safety investigations & reports

de Havilland Canada DHC-8-202, VH-TQX

Summary

On 19 April 2005 at about 1522 Eastern Standard Time, a Boeing
Company 747-422 (747) aircraft was en route from Sydney, NSW, to
Los Angeles, USA, on climb to flight level (FL) 310 and a de
Havilland Dash 8 (Dash) aircraft was en route from Lord Howe Island
to Sydney, maintaining FL240. The crew of the Dash had been issued
with a clearance to descend to 10,000 ft above mean sea level. The
intended tracks of the aircraft intersected at a point about 90 NM
east of Sydney.

The aircraft were under radar control by the Brisbane Centre
Ocean sector controller. The Australian Advanced Air Traffic System
(TAAATS) assessed the two aircraft as potentially being in conflict
and activated the short term conflict alert (STCA) on the air
situation display. Following activation of the STCA, the Ocean
controller saw that the aircraft were about 16 NM apart and
instructed both crews to turn their respective aircraft left in an
endeavour to maintain the minimum radar separation standard of 5
NM. Analysis of recorded data from TAAATS showed that the aircraft
passed with 4.1 NM lateral and 400 ft vertical spacing. The
required minimum vertical separation standard was 1,000 ft. There
was an infringement of separation standards.

The controller had been operating in the position for about 50
minutes prior to the occurrence. The level of complexity within the
sector was reported to be light to moderate. The controller
reported that despite reviewing the aircraft's tracks he expected
the track of the 747 to be northwest of the inbound track of the
Dash 8. Immediately prior to the activation of the STCA the
controller was not monitoring the aircraft situation display as he
was discussing operational coordination issues with an operational
supervisor, who was consulting a chart located near the Ocean
sector console position. The controller had initiated the
discussion with the supervisor to follow up previous correspondence
on the issue.

A review of breakdown of separation occurrences, conducted by
Airservices Australia in June 2003, found that 92 percent of en
route sector infringements of separation standards involved an
error in either building or maintaining situational awareness by
the controllers involved. The review made 31 recommendations and
Airservices Australia has implemented all the recommendations of
the review.

Analysis

In this occurrence, the controller did not perceive the
potential conflict between the aircraft, despite previous refresher
training that should have assisted in the task.

Although the presence of the supervisor in the operations room
created an opportunity to discuss an operational issue, it was not
a priority. The controller should have discussed the issue at some
other time when he was not responsible for an operational position.
The supervisor was also in a position to defer the discussion with
the controller, until a more suitable time or location, which would
have reduced the likelihood of compromising operations.

While distraction could not be discounted as a contributing
factor, the circumstances of the occurrence are consistent with the
findings of the Airservices Australia June 2003 review,
particularly with respect to low levels of situational awareness by
controllers. Over time, the benefits of the implementation of the
review recommendations in helping to develop controller awareness
of potential performance limitations should become apparent.

Safety Action

Airservices Australia safety action

The post implementation review by Airservices Australia of the
June 2003 review of breakdown of separation occurrences found that
since the recommendations were implemented, errors in either
building or maintaining situational awareness by the controllers
involved had reduced to 44 percent of occurrences involving
infringements of separation standards.